Valves formed from an inert, corrosion resistant thermoplastic material are well suited for use in chemical engineering systems. These corrosion resistant thermoplastic valves can be used with pipes or tubing formed from the same or similar material to accommodate and precisely control the flow of polycorrosive chemicals. For example, valves of this type often are used to accommodate and control the flow of sulfuric acid, nitric acid and other oxidizing chemicals as well as caustics, solvents and halogens and other problem materials at temperatures to 250.degree. F., pressures to 150 psi and flows of up to 18,500 gpm.
Valves and pipes used in corrosive liquid systems, as described herein are typically formed from polyvinyl chloride (PVC) or a chlorinated polyvinyl chloride (CPVC). For certain uses, valves and pipes may also be formed from polypropylene or polyvinylindene fluoride (PVDF).
The chemical engineering systems in which these corrosion resistant thermoplastic valves are used often require precise on-off functioning of one or more valves. The valves employed to carry out these on-off functions are typically ball valves. In many instances, the success of a particular chemical engineering operation depends upon the precise mode change from opened-to-closed or from closed-to-open. Mode changes on ball valves require the rotation of the valve stem through a 90.degree. angle. A rotation of something other than 90.degree. will result in a valve that is either not completely closed or not entirely opened. Thus, rotation of a valve stem on a ball valve through an angle either less than or greater than 90.degree. could result in a continued small flow of a particular corrosive chemical during periods when that chemical is no longer required. Conversely, certain improper rotations of the valve stem on a ball valve could result in a less than optimum flow of a particular corrosive chemical when full flow is required.
Thermoplastic valves of the type used in chemical engineering systems may be manually actuated by a pipeline operator, or they may be automatically actuated from a remote location. Manually actuated valves include handles which communicate with the valve stem to rotate the valving member through mode changes. Continuous manual service over long periods of time could degrade the connection between the handle and the stem. Consequently, the handle may slip relative to the stem thereby causing undetected incomplete rotations of th valving member. Automated valves may be electrically actuated through gear trains or linkage mechanisms. Continuous service over long periods of time could result in wear of these mechanical parts. Consequently, the valving member may not achieve complete mode changes when optimum flow of chemicals is required. Furthermore, automated valves rely upon electrical circuitry that may fail due to short circuits, thereby resulting in undetected inoperative valving members.
An additional factor that may influence the success of a particular chemical engineering operation is the generation of turbulent flow patterns in the corrosive chemicals passing through the piping system. In general, turbulent flow is generated by pipe friction and sudden expansions or contractions in the piping system. Turbulence may be caused by wear or damage to pipes, O-rings or valve seats due to the action of chemicals therein. Turbulence may also occur at fittings or valves. Turbulent flow results in head losses which vary as the square of the velocity. Turbulence in the piping system may result in a less than optimum flow of a particular corrosive chemical when full flow is required. In most instances, head losses are determined experimentally through data retrieval. However, equipment for measuring pressure adds to the system cost. Furthermore, the corrosive fluid in these systems can eventually affect the performance of pressure measuring means.
A further concern associated with chemical engineering operations is safety. In particular, leak detection and prevention is an essential element of any chemical operation since a leak occurring in a piping system carrying caustics or oxidizing chemicals could cause severe injury or even loss of life. In general a leak in a piping system will likely occur at pipe couplings which are usually associated with valves.
The prior art includes valves for medicinal fluids that are intended to enable a doctor or medical technician to visually observe the flow of fluid therethrough. U.S. Pat. No. 3,916,948 entitled "CONTROL VALVES FOR MEDICINAL PURPOSES" which issued to Benjamin on Nov. 4, 1975 discloses a version of a check valve for use in catheters for controlling the flow of body fluids. The valve has at least three flexible tubes made of a material which is at least partially transparent. The flexible tubes are connected together and form an intercommunicating central crossover. A solid ball defining an outside diameter greater than the inside diameter of the tubes is engageable within either of the tubes, and is held in the selected tube by the elasticity of the flexible plastic. The solid ball may be moved from one flexible tube to the next by squeezing the tubes. The transparency of the housing disclosed in U.S. Pat. No. 3,916,948 enables the doctor or medical technician to determine which flexible tube the ball is in. The elastic valve disclosed in U.S. Pat. No. 3,916,948 is unsuitable for use in the regulation of high pressure and high temperature flows of corrosive chemicals and caustics.
U.S. Pat. No. 4,210,174 entitled "POSITIVE PRESSURE VALVES" which issued to Eross on July 1, 1980 discloses a positive pressure valve for use in ventilators, anesthesia machines, resuscitators, and other inhalation therapy devices where it is desired to place a controlled pressure on a patient's lungs. The valve disclosed in U.S. Pat. No. 4,210,174 basically comprises a cylindrical clear plastic housing with a side arm at one end providing an inlet port and a side arm at the other end forming an outlet. A magnet is disposed in the flow path of the valve housing and exerts a pulling force on a metallic portion of a solid valving disc to urge the disc into a valve seat. The valve disclosed in U.S. Pat. No. 4,210,174 is unsuitable for use in the regulation of corrosive chemicals and caustics since it employs metallic parts that would corrode in a chemical engineering system.
The transparent medicinal fluid control devices described in the prior art do not providing visible leak detection at connective fittings.
Therefore, it is an object of the subject invention to provide a ball valve assembly which enables an observer to visually detect leaks which may occur proximate to improperly sealed fittings or damaged O-rings.
It is another object of the subject invention to provide a ball valve assembly which enables an observer to visually detect turbulent flow patterns in the fluid passing therethrough so as to ensure the efficient operation of a chemical engineering operation.
It is a further object of the subject invention to provide a ball valve assembly which enables an observer to visually ensure precise on-off mode changes and positioning of the valving member.